Many materials such as thermoplastic film, metal foil, and flattened thermoplastic tubing are manufactured in a sheet-like form and in order to form a useful product from the material it is necessary to seal the sheet-like material to itself or to a similar material. If the material is thermoweldable or heat fusible it may be sealed to itself or a similar material by the proper application of energy which raises the temperature of the material to its welding or fusing temperature. Thermoplastic sheets such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, etc. are readily heat sealable or heat weldable; and, in the prior art, sealing or welding has been accomplished by pressing two sheets of thermoplastic film together between heated seal bars, by mechanically pressing the sheets together and applying radio frequency energy, and by applying heated and compressed air blown through two opposite nozzles to seal the material together. One example of this latter described method is set forth in U.S. Pat. No. 3,278,358 which issued on Oct. 11, 1966 to Horst Rosewicz et al. An earlier example of forming heat seals by directing opposed currents of warm gas against opposed exterior surfaces of thermoplastic materials to bring them to their temperature of fusion is disclosed in U.S. Pat. No. 2,423,327 which issued on July 1, 1947 to A. B. Haslacher. Other prior art showing the use of heated air as a source of energy for welding thermoplastic surfaces together are U.S. Pat. No. 2,978,008 which issued on Apr. 4, 1961 to John D. Conti and U.S. Pat. No. 3,488,244 which issued on Jan. 6, 1970 to J. G. Lepisto. While a process employing heated air will seal together two thermoplastic surfaces such a process is relatively slow for industrial processes as the heated air must transfer heat to the thermoplastic material at its surface where heat transfer efficiency is low, and then all of the heat energy must be conducted from the surface across the entire interior of the material before it will heat to its flow or fusing temperature. The process of conduction from the surface to the interior for a thermoplastic material is a relatively slow one. Accordingly, it is one object of the present invention to provide a process which is rapid and does not depend upon heat conduction in order to produce a thermoweld.
Certain forms of radiant energy such as laser beams of certain wave lengths and electron beams will rapidly heat the entire volume of the irradiated material to its welding temperature. However, mechanical clamps or other means of holding sheets of thermoweldable material in close contact tend to interfere with the radiant energy beam and prevent complete irradiation of the target area. Accordingly, it is another object of the present invention to provide a method of holding sheets of thermoweldable material together which does not interfere with the irradiation of the material by radiant energy.
The accomplishment of the foregoing and other objects will be apparent to those skilled in the art from the following Summary of the Invention and Detailed Description of the preferred embodiments.